Nitric oxide (NO) is biosynthesized from L-arginine as the substrate by NO synthase (NOS). Currently three isozymes of NOS have been found: the brain isozyme (bNOS), the endothelial isozyme (eNOS), and the inducible isozyme (iNOS) (Moncada, S. and Higgs, A. (1993) N. Eng. J. Med. 329: 2002-2012). The transcription of iNOS can be activated by an action of endotoxins and cytokines on macrophage, vascular smooth muscle cells, hepatic cells, chondrocytes, gliacytes, etc., resulting in expression thereof (Forstermann, U., Gath, I., Schwarz, P., Closs, E. I. and Kleinert, H. (1995) Biochem. Pharmacol. 50: 1321-1332).
The iNOS has been reported to be induced by inflammatory conditions regardless of the species, and the suppression of the enzymatic activity and of the expression has been shown to be useful for amelioration of the disease states (Cattell, V. and Jansen, A. (1995) Histochem. J. 27: 777-784; Nussler, A. X. and Billiar, T. R. (1993) J. Leukoc. Biol. 54: 171-178).
It has been reported that arginine derivatives or aminoguanidine exhibit pharmacological effects in model animals of myocarditis, cerebral infarction, arthritis, sepsis, multiple sclerosis, systemic lupus erythematosus, and insulin-dependent diabetes mellitus (Moncada, S. and Higgs, E. A. (1995) Faseb. J. 9: 1319-1330). Though L-N-monomethyl arginine, a NOS inhibitor, is highly toxic at high doses, it not only improves low blood pressure in sepsis but has a marked preventive effect, on which a clinical trial is under way (Moncada, S. and Higgs, E. A. (1995) Faseb. J. 9: 1319-1330).
Furthermore, resistance against sepsis or inflammation induced by carageenin has been shown in experiments using iNOS knockout mice, revealing that the expression of iNOS causes these pathological states (Wei, X. Q., Charles, I. G., Smith, A., Ure, J., Feng, G. J., Huang, F. P., Xu, D., Muller, W., Moncada, S. and Liew, F. Y. (1995) Nature 375: 408-411).
An excess of NO produced by the induction of iNOS expression is believed to damage normal cells and cause various disease states. On the other hand, the constitutively occurring NOS(CNOS) termed eNOS or bNOS is required to suppress an increase in blood pressure and to maintain it. Thus, inhibitors which do not inhibit the activity of cNOS and that are specific for iNOS are required. However, since the regions of the proteins that regulates the enzymatic activity of isozymes are very similar to one another in the primary structure, no NOS inhibitors have yet been found which are sufficiently specific (Ogden, J. E. and Moore, P. K. (1995) Trends Biotechnol. 13: 70-78, Manning, R., Jr., Hu. L., Mizelle, H. L., Montani, J. P. and Norton, M. W. (1993) Hypertension 22: 40-48).
As enzyme inhibitors, L-arginine (and amino acid) derivatives have mainly been developed but many of them are low in isozyme specificity. Although aminoguanidine and amidine derivaties, though weakly effective, have been reported to have relatively iNOS-specific inhibitory effects (Southan, G. J. and Szabo, C. (1996) Biochem. Pharmacol. 51: 383-394), pharmaceutical agents having adequate specificity have yet not to be found.
On the other hand, TNF-α, a cytokine produced by various cells including macrophage, is believed to be an important mediator of inflammation (Vassalli, P. (1992) Annu. Rev. Immunol. 10: 411-452). There is growing evidence that the excessive production of TNF-α damages normal cells and causes various pathological conditions (Muto, Y., Nouri-Aria, K. T., Meager, A., Alexander, G. J., Eddleston, A. L. and Williams, R. (1988) Lancet 2: 72-74, Sharief, M. K. and Hentges, R. (1991) N. Engl. J. Med. 325: 467-472).
Increases in TNF-α have been observed in the synovial fluid and the blood of patients with, for example, rheumatoid arthritis (Tetta, C., Camussi, G., Modena, V., Di Vittorio, C. and Baglioni, C. (1990) Ann. Rheum. Dis. 49: 665-667; Venn, G., Nietfeld, J. J., Duits, A. J., Brennan, F. M., Arner, E., Covington, M., Billingham, M. E. and Hardingham, T. E. (1993) Arthritis Rheum. 36: 819-826). Antibody against TNF-α has also been demonstrated to be effective in clinical trials (Elliott, M. J., Maini, R. N., Feldmann, M., Long-Fox, A., Charles, P., Bijl, H. and Woody, J. N. (1994) Lancet 344:1125-1127; Elliott, M. J., Maini, R. N., Feldmann, M., Kalden. J. R., Antoni, C., Smolen, J. S., Leeb, B., Breedveld, F. C., Macfarlane, J. D., Bijl, H. and et al. (1994) Lancet 344:1105-1110; Rankin, E. C., Choy, E. H., Kassimos, D., Kingsley, G. H., Sopwith, A. M., Isenberg, D. A. and Panayi, G. S. (1995) Br. J. Rheumatol. 34: 334-342).
Furthermore, the involvement of TNF-α in sepsis or inflammatory bowel diseases has been pointed out and the ameliorating effects of anti-TNF-α antibody on these diseases have been observed (Vincent, J. L., Bakker, J., Marecaux, G., Schandene, L., Kahn, R. J. and Dupont, E. (1992) Chest 101: 810-815; Hinshaw, L. B., Tekamp-Olson, P., Chang, A. C., Lee, P. A., Taylor, F., Jr., Murray, C. K., Peer, G. T., Emerson, T., Jr., Passey, R. B. and Kuo, G. C. (1990) Circ. Shock 30: 279-292).
These findings expressly indicate that the excessive production of TNF-α causes and aggravates various inflammations, and thereby there the development of pharmaceutical agents which can inhibit the production of TNF-α is required (Nyman, U., Mussener, A., Larsson, E., Lorentzen, J. and Klareskog, L. (1997) Clin. Exp. Immunol. 108: 415-419).
Thus, iNOS or TNF-α have been recognized to be one of the causes of various inflammations. However, the fact that many other mediators have been demonstrated to cause inflammation and thereby the cause of the diseases cannot be attributed to any one particular mediator makes the development of therapeutic agents difficult. Under these circumstances, there is a great need for low molecular weight compounds that not only suppress the expression of particular proteins but inhibit widely the production and expression of proteins involved as causative factor in the inflammation.
NF-κB is a protein that regulates gene expression and is one of the so-called transcription factors. When normal cells are stimulated with an inflammatory cytokine such as interleukin-1 (IL-1) and TNF-α, a lipopolysaccharide, or ultraviolet rays, NF-κB are activated and then they translocate from the cytoplasm into the nucleus where they bind to specific nucleotide sequences on the genomic DNA and thereby become involved in the expression of various genes (Blackwell, T. S. and Christman, J. W. (1997) Am. J. Respir. Cell Mol. Biol. 17: 3-9).
Genes encoding iNOS and TNF-α, though entirely different from one another, have regions to which NF-κB binds on the expression control region of the genomic gene thereof, and there is growing evidence that the activation of NF-κB is important for the expression of these proteins in common (Jongeneel, C. V. (1994) Prog. Clin. Biol. Res. 388: 367-381; Xie, Q. W., Kashiwabara, Y. and Nathan, C. (1994) J. Biol. Chem. 269: 4705-4708; Nunokawa, Y., Oikawa, S. and Tanaka, S. (1996) Biochem. Biophys. Res. Commun. 223: 347-352).
Many genes that are involved in immunological inflammatory reactions under expression control by NF-κB are recognized, in addition to iNOS and TNF-α, ones for inflammatory cytokines such as IL-1, IL-6 and IL-8, as well as cell adhesion factors such as ICAM-1, VCAM-1 and ELAM-1 or the like (Collins, T., Read, M. A., Neish, A. S., Whitley, M. Z., Thanos, D. and Maniatis, T. (1995) Faseb. J. 9: 899-909). Furthermore, it is known that inflammatory cytokines, when bound to receptors, transduce NF-κB-activating signals via various routes, and this fact is believed to be cause that further aggravates inflammation. Thus, the activation of NF-κB in inflammation is understood as an etiological and aggravating matter of diseases (Baeuerle, P. A. and Baichwal., V. R. (1997) Adv. Immunol. 65: 111-137).
In recent years, it has also been reported that HIV, HTLV-1, CMV, adenovirus and the like activate NF-κB in host cells (Dezube, B. J., Pardee, A. B., Beckett, L. A., Ahlers, C. M., Ecto, L., Allen-Ryan, J., Anisowicz, A., Sager, R. and Crumpacker, C. S. (1992) J. Acquir. Immune Defic. Syndr. 5: 1099-1104; Nabel, G. and Baltimore, D. (1987) Nature 326: 711-713; Fazely, F., Dezube, B. J., Allen-Ryan, J., Pardee, A. B. and Ruprecht, R. M. (1991) Blood 77: 1653-1656; Munoz, E. and Israel, A. (1995) Immunobiology 193: 128-136). The activation of NF-κB in turn activates its transcription leading to the progression of viral propagation and infection.
Accordingly, it is possible to suppress altogether the induction of expression of these inflammatory cytokines, genes of adhesion molecules, and viruses by inhibiting the activation of NF-κB, and NF-κB inhibitors are promising as therapeutic agents of such diseases as are caused either directly or indirectly by the activation of NF-κB, specifically various inflammatory diseases, autoimmune diseases and viral diseases, and immunosuppressive agents.
Therapeutic agents currently used for chronic diseases include steroid hormones such as glucocorticoids, non-steroidal aspirin formulations, and the like. However, glucocorticoids are known to be associated with the appearance of severe side effects such as the aggravation of infectious diseases, onset of peptic ulcer, and central effects, and therefore are not amenable to a long-term administration. Furthermore, although the non-steroidal agents, suppress the production of prostaglandins etc., they do not provide curative treatments and they are known to exhibit such side effects as the onset of peptic ulcer and central effects.
It has also been reported in recent years that anti-inflammatory drugs at high doses inhibit the activation of NF-κB (Auphan, N., DiDonato, J. A., Rosette, C., Helmberg, A. and Karin, M. (1995) Science 270: 286-290; Shackelford, R. E., Alford, P. B., Xue, Y., Thai, S. F., Adams, D. O. and Pizzo, S. (1997) Mol Pharmacol. 52: 421-429; Bitko, V., Velazquez, A., Yang, L., Yang, Y. C. and Barik, S. (1997) Virology 232: 369-378). However, due to their diverse pharmacological actions, these compounds have side effects, and therefore the development of safer drugs based on a novel mechanism is required.
As a method of inhibiting the actions of TNF-α, it is thought that the use of antibodies that specifically bind to TNF-α and TNF receptor proteins. However, those are both macromolecule proteins and are not suitable for oral administration.
Phenylmethyl benzoquinone derivatives exhibit the effect of improving cerebral functions in experimental animals of anoxia at low doses, and are shown to be effective for improving and treating intracerebral organic disorders and mental function disorders (Suzuki, K., Tatsuoka, T., Murakami, T., Ishihara, T., Aisaka, K., Inoue, T., Ogino, R., Kuroki, M., Miyazaki, T., Satoh, F., Miyano, S. and Sumoto, K. (1996) Chem. Pharm. Bull. 44: 139-144). However, at present the effects of phenylmethyl benzoquinone derivatives on the production of inflammatory mediators and on the activation of NF-κB have not been known.